Braking force controller

ABSTRACT

A braking force controller includes: a target jerk calculation unit; a first estimation unit configured to estimate an increment of braking force when a prescribed factor that increases braking force to be generated by the first actuator unit currently occurs; a second estimation unit configured to estimate the increment of the braking force when the prescribed factor occurs within a prescribed period; and a control unit configured to determine a negative jerk generated when the second actuator unit generates the braking force such that a sum of the negative jerk and the jerk generated by the first actuator unit without the prescribed factor becomes the target jerk. When the increment of the braking force due to the prescribed factor is larger than a prescribed value, the control unit corrects the determined negative jerk such that an absolute value of the negative jerk becomes smaller.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2019-077358 filed onApr. 15, 2019 including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND 1. Technical Field

The present disclosure relates to a braking force controller mounted ona vehicle to control braking force of the vehicle.

2. Description of Related Art

In the field of vehicles, various kinds of techniques are proposed forimproving ride comfort and operation feeling. For example, JapanesePatent Application Publication No. 10-280990 discloses a fuel cutcontroller. When fuel cut is prohibited during braking of a vehicle toprevent catalyst from deteriorating under high temperature condition,the fuel cut controller compensates braking force by using analternator, an air-conditioner, a brake, a gearshift, or the like, toacquire a desired braking force. Japanese Patent Application PublicationNo. 2006-297994 discloses an integrated vehicle control apparatus. Theintegrated vehicle control apparatus distributes control targets,determined based on the amount of operation by a user, to a drive systemand a control system in accordance with a charge ratio. The integratedvehicle control apparatus also transmits the control targets beforedistribution to a stabilization system to cause the stabilization systemto perform a correction process, for the purpose of eliminating thenecessity of the stabilization system to synchronize values of thedistributed control targets so as to reduce delay and improveresponsiveness with respect to operation.

SUMMARY

For adequate ride comfort and operation feeling in a vehicle, it isdesirable to provide a user with adequate deceleration feeling, when,for example, the user stops operating an accelerator pedal, and therebythe vehicle shifts to a coasting state where neither the acceleratorpedal nor a brake pedal is operated.

Factors of the adequate deceleration feeling include decreasing negativeacceleration when the travel direction of the vehicle is defined as apositive direction (increasing an absolute value of acceleration in adeceleration direction of the vehicle), as well as decreasing negativejerk when the travel direction of the vehicle is defined as a positivedirection (quickly increasing the absolute value of acceleration in thedeceleration direction of the vehicle). Accordingly, the adequatedeceleration feeling may be achieved by decreasing the negative jerk.Jerk j is defined as a third-order differentiation of (j=d³x/dt³)position x by time t. The jerk J is expressed in the unit of, forexample, [meter per second per second per second (m/s³)]. As is clearfrom the definition, the jerk is the rate of change of acceleration.

In the coasting state, negative jerk is caused by decrease in driveforce (increase in braking force) generated in an engine or atransmission. However, by making the brake or the like generate thebraking force, the negative jerk can further be decreased, and thedeceleration feeling can be enhanced as described before.

However, when gear shifting by the transmission or the like increasesthe braking force, while the brake generates negative jerk, the negativeacceleration and negative jerk generated in the vehicle degrease beyondan adequate range, which may rather deteriorate the ride comfort andoperation feeling.

The present disclosure has been made in view of the above-statedproblem, and it is an object of the present disclosure to provide abraking force controller capable of achieving adequate ride comfort andoperation feeling while the vehicle is in a coasting state.

In order to solve the problem, one aspect of the present disclosurerelates to a braking force controller mounted on a vehicle including afirst actuator unit and a second actuator unit configured to generatebraking force. The braking force controller is configured to control thebraking force to be generated by the second actuator unit, when anoperation amount of an accelerator pedal shifts to zero from other thanzero, and the vehicle is put in a coasting state because of theoperation amount of the brake pedal being zero. The braking forcecontroller includes a target jerk calculation unit, a first estimationunit, a second estimation unit, and a control unit. The target jerkcalculation unit is configured to calculate a target jerk that is ageneration target value of jerk when the braking force is generated inthe vehicle, the jerk being negative when a vehicle travel direction isdefined as a positive direction. The first estimation unit is configuredto determine whether or not a prescribed factor that increases thebraking force generated by the first actuator unit currently occurs, andto estimate, when determining that the prescribed factor occurs, anincrement of the braking force due to the prescribed factor. The secondestimation unit is configured to determine whether or not the prescribedfactor occurs within a prescribed period from present time even when theprescribed factor does not currently occur in the vehicle, and toestimate, when determining that the prescribed factor occurs, anincrement of the braking force due to the prescribed factor. The controlunit is configured to determine, based on a calculation result of thetarget jerk calculation unit, that a sum of the negative jerk generatedwhen the second actuator unit generates the braking force and the jerkgenerated by the first actuator unit when the prescribed factor does notincrease the braking force becomes the target jerk. When the prescribedfactor currently occurs or occurs within the prescribed period, and theincrement in the braking force due to the prescribed factor is largerthan a prescribed value, the control unit corrects the determinednegative jerk such that an absolute value of the negative jerk becomessmaller, based on an estimation result of the first estimation unit orthe second estimation unit.

The present disclosure can provide the braking force controller capableof achieving adequate ride comfort and operation feeling in a vehicle ina coasting state.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments will be described below with reference to theaccompanying drawings, in which like numerals denote like elements, andwherein:

FIG. 1 is a block diagram showing a braking force controller accordingto an embodiment of the present disclosure;

FIG. 2 shows a process according to the embodiment of the presentdisclosure;

FIG. 3 shows an example of a map of target jerk according to theembodiment of the present disclosure;

FIG. 4 shows an example of the map of the target jerk according to theembodiment of the present disclosure;

FIG. 5 shows an example of the map of the target jerk according to theembodiment of the present disclosure;

FIG. 6 shows an example of the characteristics of an increment ofbraking force according to the embodiment of the present disclosure;

FIG. 7 shows another an example of the characteristics of the incrementof braking force according to the embodiment of the present disclosure;

FIG. 8 shows an example of the characteristics of the increment ofbraking force according to the embodiment of the present disclosure;

FIG. 9 shows an example of the characteristics of the increment ofbraking force according to the embodiment of the present disclosure;

FIG. 10 shows an example of control characteristics of a transmissionaccording to the embodiment of the present disclosure; and

FIG. 11 shows an example of control according to the embodiment of thepresent disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

The braking force controller according to the present disclosurecontrols jerk generated in a brake or the like to achieve decelerationfeeling assumed to be expected by a user in a coasting state of avehicle, and thereby achieves adequate ride comfort and operationfeeling of the vehicle. In the disclosure, when braking force increasesdue to gear shifting of a transmission, or the like, in the coastingstate, the jerk generated in the brake or the like is reduced in orderto reduce fluctuation in deceleration feeling and to restrain the ridecomfort and the operation feeling from deteriorating.

Embodiment

Hereinafter, an embodiment of the present disclosure will be describedin detail with reference to the drawings. Parameters such as speed,acceleration, drive force, and jerk, are expressed by signed values thatare positive in the direction where a vehicle travels. When negativedrive force is referred to as braking force, the braking force isexpressed by an absolute value.

Configuration

FIG. 1 shows the configuration of a braking force controller 100 andperipheral devices according to an embodiment of the present disclosure.The braking force controller 100 is mounted on a vehicle. A firstactuator unit 200 includes, for example, an engine and a transmission. Asecond actuator unit 300 includes, for example, a brake. While the firstactuator unit 200 can generate braking force relatively stably in acoasting state, the braking force may increase independently of thecontrol of the braking force controller 100, due to a prescribed factorcaused by control from other control systems of the vehicle, such asgear shifting in the transmission. The second actuator unit 300 includesone or more prescribed actuators for generating the braking force. Forproviding adequate deceleration feeling for a user in the coastingstate, the braking force controller 100 can control the second actuatorunit 300 to generate braking force for compensating the braking forcegenerated by the first actuator unit 200. The first actuator unit 200and the second actuator unit 300 may each include any type and anynumber of actuators as long as the actuators have the characteristics asdescribed above.

The first actuator unit 200 and the second actuator unit 300 eachinclude a control unit configured to perform various processes regardingthe actuators included in each of the actuator units. A sum total of thedrive force generated by the respective actuators included in the firstactuator unit 200 and the second actuator unit 300 serves as total driveforce for driving the vehicle. Acceleration and jerk of the vehicle eachfluctuate in accordance with the sum of the braking force generated bythe respective actuators and a sum of change rates of the braking force.When the respective actuators generate braking force, the actuatorscontribute to the acceleration and the jerk of the vehicle. Thiscontribution is expressed as the actuators generating the accelerationand the jerk of the vehicle. When the vehicle travels along an uphillroad or a downhill road, a signed constituent of gravity along thetravel direction is further added to the total drive force.

The braking force controller 100 includes a target jerk calculation unit101, a first estimation unit 102, a second estimation unit 103, and acontrol unit 104.

In order to generate braking force in the coasting state, the targetjerk calculation unit 101 calculates target jerk as a jerk generationtarget value that is negative when the travel direction of the vehicleis defined as a positive direction.

The first estimation unit 102 determines whether or not a prescribedfactor, which increases the braking force generated by the firstactuator unit 200, currently occurs. When determining that theprescribed factor occurs, the first estimation unit 102 estimates anincrement of the braking force.

The second estimation unit 103 determines whether or not the prescribedfactor, which increases the braking force generated by the firstactuator unit 200, occurs within a prescribed period from present time,i.e., in the near future, although the prescribed factor does notcurrently occur. When determining that the prescribed factor occurs inthe near future, the second estimation unit 103 estimates an incrementof the braking force.

The control unit 104 determines negative jerk to be generated by thesecond actuator unit 300, based on a calculation result of the targetjerk calculation unit 101. In the case where the prescribed factorcurrently occurs, and the case where the prescribed factor may occurwithin a prescribed period from present time although it does notcurrently occur, and the increment of the braking force is larger than aprescribed value, the control unit 104 corrects the determined negativejerk such that an absolute value of the negative jerk becomes smaller,based on an estimation result of the first estimation unit 102 or thesecond estimation unit 103. The control unit 104 instructs the secondactuator unit 300 to generate the thus-calculated negative jerk. Thecontrol unit 104 also executes and controls other various kinds ofprocesses of the braking force controller 100.

Process

FIG. 2 is a flowchart illustrating an example of a process executed bythe braking force controller 100. With reference to FIG. 2, an exampleof acceleration control by the braking force controller 100 will bedescribed. The process is executed in the state where the vehicle isturned on to enable travel by user operation.

(Step S101): the control unit 104 constantly acquires the amount ofaccelerator pedal operation by a user detected by an accelerator pedalsensor included in the vehicle and the amount of brake pedal operationby the user detected by the brake pedal sensor. Based on the acquiredoperation amounts of the accelerator pedal and the brake pedal, thecontrol unit 104 detects a shift from the state where the user operatesthe accelerator pedal (the operation amount is not equal to zero) to thestate where the user does not operate the accelerator pedal (theoperation amount is equal to zero) and the user does not operate thebrake pedal (the operation amount is equal to zero). As a result, thecontrol unit 104 detects that the vehicle is in a coasting state. Whenthe control unit 104 detects the coasting state, the process proceeds tostep S102. When the control unit 104 does not detect the coasting state,the control unit 104 repeats step S101 and waits for the vehicle to bein the coasting state. In the present step, the control unit 104typically detects the coasting state that is established when theaccelerator pedal operation is released as described above. However, thecontrol unit 104 may also detect the coasting state established when thebrake pedal operation is released.

(Step S102): the target jerk calculation unit 101 calculates target jerkthat is a target value of the negative jerk to be generated in thevehicle in the coasting state. The target jerk is assumed to be able topresent adequate deceleration feeling to the user when the coastingstate is established. The target jerk is calculated by a predeterminedmethod. The target jerk calculation unit 101 may calculate the targetjerk by acquiring from sensors or other devices the informationnecessary for calculating the target jerk, or may acquire the targetjerk calculated by other devices.

Examples of the calculation method of the target jerk will be described.In each of the examples, a map is used in which target acceleration ispredetermined for each speed of the vehicle. FIGS. 3, 4, and 5schematically show the maps in the respective examples.

In an example shown in FIG. 3, the target jerk becomes smaller, as thespeed of the vehicle becomes larger. Specific values can be determinedbased on evaluation performed by an experiment or the like.

In an example shown in FIG. 4, consideration is given to drive modesrepresenting traveling characteristics specified by the user, as well asto the speed of the vehicle. When the drive mode is an eco-mode whichspecifies a travel with low fuel consumption, the target jerk is set tobe larger than the target jerk at the same speed in a normal mode, whichis a drive mode other than the eco-mode. For example, the map shown inFIG. 3 may be used in the normal mode. The map in the eco-mode shown inFIG. 4 may be prepared by multiplying the value of the target jerkaccording to the map shown in FIG. 3 by a positive coefficient α that issmaller than one. Similarly, when the drive mode is a sport mode whichspecifies a sporty travel, the target jerk may be set to be smaller thanthat in the normal mode at the same speed.

In an example shown in FIG. 5, consideration is given to a road surfacegradient, in addition to the speed of the vehicle. When the road surfaceis a downhill road, the target jerk is set to be smaller than that inthe case of a flat road at the same speed. For example, the map shown inFIG. 3 may be used in the case of the flat road, and the map in thedownhill road shown in FIG. 5 may be prepared by multiplying the valueof the target jerk according to the map shown in FIG. 3 by a coefficientβ that is larger than one.

When the road surface is an uphill road, the target jerk is set to belarger than that in the case of the flat road at the same speed. Forexample, the map shown in FIG. 3 may be used in the case of the flatroad, and the map in the uphill road may be prepared by multiplying thevalue of the target jerk according to the map in FIG. 3 by a coefficientγ that is smaller than one.

The target jerk may also be calculated based on both the drive mode andthe road surface gradient. For example, the map shown in FIG. 3 may beused in the case of the flat road and the normal mode, and a map in theuphill road and the eco-mode may be prepared by multiplying the value ofthe target jerk according to the map shown in FIG. 3 by the coefficientα and the coefficient β. Similarly, a map in the uphill road and theeco-mode may be prepared by multiplying the value of the target jerkaccording to the map shown in FIG. 3 by the coefficient α and thecoefficient γ.

For calculation of the target jerk, various kinds of information outputfrom various sensors and an electronic control unit (ECU) included inthe vehicle is used. In the above examples, the calculation method ofthe target jerk, using the speed of the vehicle and further usinginformation indicating the drive mode specified by the user or thegradient of the road surface, is not particularly limited. A basic mapmay be prepared as described above, and the target jerk may becalculated by multiplying the target jerk by different coefficients inaccordance with the state of the vehicle or the periphery thereof, or byusing maps individually prepared for respective states in advance.Alternatively, when the presence of another vehicle is detected aprescribed distance ahead of the vehicle by, for example, a camera and aradar, the information indicating the presence may be acquired to setthe target jerk smaller than the case without the presence of anothervehicle at the same speed.

(Step S103): the control unit 104 determines whether or not to cause thesecond actuator unit 300 to generate jerk. First, the control unit 104acquires from the first actuator unit 200 a negative jerk j1 that thefirst actuator unit 200 can currently generate. When the first actuatorunit 200 includes, for example, an engine and a transmission, thecontrol unit of the first actuator unit 200 can calculate the jerk j1based on an engine throttle opening (zero in the coasting state), and acurrent gear stage of the transmission, for example. The jerk j1 is thejerk assumed when the operating state of the first actuator unit 200,such as the gear stage, is maintained unchanged from the current state.

Next, the control unit 104 compares the jerk j1 with the target jerk Jcalculated in step S102 to determine whether or not to cause the secondactuator unit 300 to generate negative jerk. When the jerk j1 is equalto or less than the target jerk J, the first actuator unit 200 generatessufficient negative jerk. Accordingly, the control unit 104 determinesto prevent the second actuator unit 300 from generating the negativejerk. Then, the process proceeds to step S101, where the control unit104 waits until the coasting state is restarted.

When the jerk j1 is larger than the target jerk J, the negative jerk tobe generated by the first actuator unit 200 is short of the target jerk.Accordingly, the control unit 104 determines to cause the secondactuator unit 300 to generate negative jerk. The process proceeds tostep S104.

(Step S104): the control unit 104 determines whether or not a prescribedfactor, which increases the braking force generated by the firstactuator unit 200, currently occurs. For example, when the firstactuator unit 200 includes a transmission, examples of the prescribedfactor may include gear shifting by the control from other controlsystems, and reduction in output torque caused by engagement of alock-up clutch included in the transmission. For example, the controlunit 104 can acquire information indicating whether or not such aprescribed factor currently occurs from the control unit of the firstactuator unit 200, and can use the information for determination. Whenthe control unit 104 determines that the prescribed factor occurs, theprocess proceeds to step S105. When the control unit 104 determines thatthe prescribed factor does not occur, the process proceeds to step S110.

(Step S105): the control unit 104 estimates an increment D of thebraking force generated by the first actuator unit 200. Examples of anestimation method will be described below.

When the first actuator unit 200 includes a transmission, and theprescribed factor includes gear shifting of the transmission, theincrement D of the braking force can be calculated, for example, basedon a gear ratio or oil temperature of the transmission. FIG. 6schematically shows a map indicating the relationship between the gearratio of the transmission and the increment of the braking force. Themap indicates that as a current gear ratio is larger, a temporaryincrement of the braking force in a transient state of the gear shiftingis larger. With reference to such a map, the control unit 104 canestimate the increment D corresponding to the gear ratio in a currentgear stage. FIG. 7 schematically shows a map indicating the relationshipbetween the oil temperature of the transmission and the increment of thebraking force. The map indicates that as a current oil temperature ofthe transmission is larger, a temporary increment of the braking forcein the transient state of the gear shifting is smaller. The control unit104 can estimate the increment D corresponding to the current oiltemperature of the transmission with reference to such a map.

When the first actuator unit 200 includes a lock-up clutch, and theprescribed factor includes engagement of the lock-up clutch, theincrement D of the braking force can be calculated based on a differencebetween the speed of the engine and the speed of the transmission on thelock-up clutch side, and on the oil temperature of the lock-up clutch,for example. FIG. 8 schematically shows a map indicating therelationship between the speed of the transmission and the increment ofthe braking force. The lock-up clutch is typically included in thetransmission. The lock-up clutch is disengaged at the start of the gearshifting. Then, the speed of the transmission on the lock-up clutch sideincreases due to gear shifting, so that the speed of the engine sidebecomes smaller than the speed of the transmission on the lock-up clutchside. When the speed of the engine side increases up to a prescribedallowable range from this state, the lock-up clutch is engaged again.The map indicates that as a difference in speed at the time ofengagement is larger, a temporary increment of the braking force at thetime of engagement is larger. The control unit 104 can estimate theincrement D corresponding to the estimated difference in speed at thetime of engagement with reference to such a map. FIG. 9 schematicallyshows a map indicating the relationship between the oil temperature ofthe lock-up clutch and the increment of the braking force. The mapindicates that as the current oil temperature of the lock-up clutch ishigher, a temporary increment of the braking force at the time ofengagement is smaller. The control unit 104 can estimate the increment Dcorresponding to the current oil temperature of the lock-up clutch withreference to such a map.

To estimate the increment D, the control unit 104 can properly acquireinformation, including current gear stage, speed, and each oiltemperature of the transmission, from the control unit of the firstactuator unit 200. As the above-stated maps, those prepared byexperiments or the like in advance can be used. The control unit 104 cancombine the above estimation methods. More specifically, the controlunit 104 can estimate the increment D based on a map which defines anincrement corresponding to two or more combinations, out of the gearstage, the speed, and each oil temperature. The estimation methods ofthe increment D are not limited to these. Appropriate estimation methodsmay be adopted in accordance with types and characteristics of theactuators of the first actuator unit 200.

(Step S106): the control unit 104 compares the increment D of thebraking force estimated in step S105 with prescribed thresholds d1(>0),d2(>d1). When the increment D is equal to or less than the threshold d1,the process proceeds to step S107. When the increment D is larger thanthe threshold d1, and is equal to or less than the threshold d2, theprocess proceeds to step S108. When the increment D is larger than thethreshold d2, the process proceeds to step S109.

(Step S107): the control unit 104 determines negative jerk to begenerated by the second actuator unit 300. In this step, for example, ajerk j2 to be generated by the second actuator unit may be set to adifference (J−j1) between the target jerk J calculated in step S102 andthe jerk j1 that can currently be generated by the first actuator unit200, the jerk j1 being acquired in step S103. The control unit 104instructs the second actuator unit 300 to generate the jerk j2 (=J−j1).The control unit 104 may calculate the value of drive force whichgradually decreases based on the jerk j2, and may sequentially indicatethe value to the second actuator unit 300. The control unit of thesecond actuator unit 300 may cause the actuator to generate theindicated drive force. Alternatively, the control unit 104 may indicatesthe jerk j2 to the second actuator unit 300. The control unit of thesecond actuator unit 300 may calculate the drive force which graduallydecreases based on the indicated jerk j2, and may cause the actuator togenerate the indicated jerk j2. In this step, when increase in thebraking force due to the prescribed factor does not occur in the firstactuator unit 200, a sum of the negative jerk j1 generated by the firstactuator unit 200 and the negative jerk j2 generated by the secondactuator unit 300 becomes equal to the target jerk J. This step isexecuted when increase in the braking force generated by the firstactuator unit 200 does not occur or when the level of the increase isrelatively small even if the increase occurs. Accordingly, the negativejerk and negative acceleration generated in the vehicle fall within anadequate range. Then, the process proceeds to step S101, where thecontrol unit 104 waits until the coasting state is restarted

(Step S108): the control unit 104 determines negative jerk to begenerated by the second actuator unit 300. In this step, the jerk j2 tobe generated by the second actuator unit may be obtained by multiplyinga value calculated as in step S107 by a positive coefficient δ that issmaller than one, for example. The control unit 104 instructs the secondactuator unit 300 to generate the jerk j2 (=α×(J−j1). Thus, in thepresent step, the negative jerk j2 generated by the second actuator unit300 is corrected such that an absolute value of the negative jerk j2becomes smaller (lower) than the negative jerk j2 obtained in step S107.The present step is executed when the degree of increase in the brakingforce generated by the first actuator unit 200 is relatively medium.When the correction is performed, the negative acceleration or thenegative jerk generated in the vehicle is less likely to become smallerthan an adequate range, and deterioration in the ride comfort or theoperation feeling can be restrained. Then, the process proceeds to stepS101, where the control unit 104 waits until the coasting state isrestarted.

(Step S109): the control unit 104 prevents the second actuator unit 300from generating negative jerk regardless of the determination of stepS103. The present step is executed when the degree of increase in thebraking force generated by the first actuator unit 200 is relativelylarge. Since the second actuator unit 300 is prevented from generatingthe negative jerk, the negative acceleration or the negative jerkgenerated in the vehicle is less likely to become smaller than theadequate range, and deterioration in the ride comfort or the operationfeeling can be restrained. Then, the process proceeds to step S101,where the control unit 104 waits until the coasting state is restarted.

(Step S110): the control unit 104 determines whether or not theprescribed factor occurs within a prescribed period from present time.Examples of the determination method will be described below.

Description is given of the method of determining whether or not gearshifting of the transmission, that is the prescribed factor, occurswithin a prescribed period, in the case where the first actuator unit200 includes the transmission. The control unit 104 can refer to a mapindicating the characteristics of transmission control of thetransmission performed by another control system. FIG. 10 shows anexample of the map. In the map shown in FIG. 10, the gear stage of thetransmission is determined based on vehicle speed and throttle opening.In acceleration of the vehicle, when the speed of the vehicle increasesto the speed corresponding to a current throttle opening in a speedshift line shown by a solid line in the map, upshifting starts. Indeceleration of the vehicle, when the speed of the vehicle decreases tothe speed corresponding to a current throttle opening in a speed shiftline shown by a dotted line in the map, downshifting starts. Since thevehicle is in a coasting state, the throttle opening is zero. Hence, thevehicle speed is maintained or decreases in principle. The control unit104 acquires a current gear stage of the transmission, and identifiesthe speed at which downshifting from the gear stage starts with thethrottle opening of zero. As a result, the control unit 104 can identifythe speed at which next gear shifting operation starts in thetransmission. In the example shown in FIG. 10, when the current gearstage is third gear, the control unit 104 identifies a speed V₃₂corresponding to the throttle opening of zero in a speed shift line ofdownshifting from third gear to second gear as the speed at which thenext gear shifting operation starts in the transmission.

The control unit 104 identifies a current vehicle speed v and anacceleration a. The speed v can be identified by properly acquiring thespeed from a speed sensor included in the vehicle or other devices. Theacceleration a can be identified by, for example, acquiring the vehiclespeed v at a plurality of time points, and calculating a time variationrate thereof. Alternatively, the control unit 104 may acquire theacceleration a from another device, such as an acceleration sensorincluded in the vehicle. The control unit 104 may identify the speed atwhich next gear shifting operation starts in the transmission based onthe current gear stage as described above. Alternatively, after thespeed v is identified, the speed at which next gear shifting operationstarts in the transmission may be identified based on the speed v andthe aforementioned map.

The control unit 104 predicts time t1 until next gear shifting operationstarts in the transmission from present time. Assuming that theacceleration a of the vehicle is constant, the control unit 104 predictstime t1 until next gear shifting operation starts in the transmissionfrom present time, based on the current speed v, speed V at which nextgear shifting operation starts in the transmission, and the accelerationa, according to an expression (1) below:

t1=(v−V)/|a|  Expression (1)

When the predicted time t1 is equal to or less than a prescribed period,the control unit 104 can determine that the prescribed factor occurswithin a prescribed period from present time. When the predicted time t1is larger than the prescribed period, the control unit 104 can determinethat the prescribed factor does not occur within a prescribed periodfrom present time.

The method of determining whether or not engagement of a lock-up clutchoccurs within a prescribed period as the prescribed factor, in the casewhere the first actuator unit 200 includes the lock-up clutch, issimilar to the method disclosed before. Since the engagement of thelock-up clutch typically occurs with gear shifting of the transmission,time t2 until next engagement of the lock-up clutch occurs can becalculated as in the case of time t1. However, the engagement of thelock-up clutch strictly occurs at the timing when the difference betweenthe speed of the engine and the speed of the transmission on the lock-upclutch side falls within an allowable range after gear shifting of thetransmission. Accordingly, time t2 may be a value obtained by adding aprescribed value to time t1, or may be calculated using a map indicatingengagement characteristics of the lock-up clutch instead of the mapshown in FIG. 10. When the predicted time t2 is equal to or less than aprescribed period, the control unit 104 can determine that theprescribed factor occurs within a prescribed period from present time.When the predicted time t2 is larger than the prescribed period, thecontrol unit 104 can determine that the prescribed factor does not occurwithin a prescribed period from present time.

When the control unit 104 determines that the prescribed factor occurswithin a prescribed period from present time by the aforementionedmethod, the process proceed to step S111. When the control unit 104determines that the prescribed factor does not occur within theprescribed period, the process proceeds to step S107. The prescribedperiod may preferably be set to a period similar to the period duringwhich the coasting state is assumed to continue. The prescribed periodmay be predetermined, or may be changed in accordance with drivingcharacteristics of the user.

(Step S111): the control unit 104 estimates an increment D′ of thebraking force generated by the first actuator unit 200. As theestimation method, a method similar to those described in step S105 maybe used.

(Step S112): the control unit 104 compares the increment D′ of thebraking force estimated in step S111 with prescribed thresholds d1′(>0),d2′(>d1′). When the increment D′ is equal to or less than the thresholdd1′, the process proceeds to step S107. When the increment D′ is largerthan the threshold d1′, and is equal to or less than the threshold d2′,the process proceeds to step S108. When the increment D′ is larger thanthe threshold d2′, the process proceeds to step S109. The thresholdsd1′, d2′ may be similar to or different from the thresholds d1, d2,respectively. For example, the thresholds d1′, d2′ may be set such thatd1′>d1, d2′>d2. The second estimation unit 103 determines whether or notthe prescribed factor occurs within a prescribed period from presenttime based on prediction. Accordingly, the determination is lower inaccuracy than the determination regarding whether or not the prescribedfactor currently occurs by the first estimation unit 102. Settingd1′>d1, d2′>d2 can reduce insufficient deceleration feeling whenprediction of the second estimation unit 103 does not come true, and canrestrain deterioration in the ride comfort or operation feeling.

When the accelerator pedal sensor and the brake pedal sensor detectoperation of the accelerator pedal or operation of the brake pedal bythe user during execution of the process of respective steps S102 toS112, the control unit 104 interrupts the process, and the processproceeds to step S101. Other control systems perform, aside from thepresent process, conventional general acceleration or decelerationcontrol corresponding to the detected operation of the accelerator pedalor the brake pedal.

The period when the second actuator unit 300 generates the negative jerkj2 ends when the coasting state of the vehicle ends. In addition, theperiod may end when, for example, the vehicle speed decreases to aprescribed positive speed or zero in the case where the coasting stateis relatively long. The prescribed positive speed can be set by a methodusing a map based on the vehicle speed or the like, like theabove-described method used for calculating the target jerk, forexample. Alternatively, the period of maintaining generation of thenegative jerk may be a predetermined prescribed period, or may variablybe set using a method similar to the above-described method forcalculating the target jerk.

Examples of the control based on the above process will be described.FIG. 11 shows graphs where horizontal axis represents time, a verticalaxis represents an operation amount of the accelerator pedal, and athick solid line represents acceleration of the vehicle. Among thegraphs indicating the relationship between acceleration and time in FIG.11, the uppermost graph indicates the case where step S107 is executedwithout occurrence of increase in the braking force of the firstactuator unit 200 due to the prescribed factor. The second uppermostgraph indicates the case where step S108 is executed with occurrence ofthe increase in the braking force of the first actuator unit 200 due tothe prescribed factor. The third uppermost graph indicates the casewhere step S109 is executed with occurrence of the increase in thebraking force of the first actuator unit 200 due to the prescribedfactor.

In the graphs of FIG. 11, dashed dotted lines further indicateacceleration corresponding to the braking force generated by the firstactuator unit 200. For comparison, thick dotted lines indicate theacceleration at the time of executing step S107 although increase in thebraking force of the first actuator unit 200 occurs due to theprescribed factor.

Until time T1, the user operates the accelerator pedal, so thatconventional control corresponding to the operation amount of theaccelerator pedal is executed, and thereby positive acceleration isgenerated.

In time T1, when the user stops accelerator pedal operation, the vehicleshifts to a coasting state where both the accelerator pedal operationand the brake pedal operation are not performed. After time T1, thebraking force is generated by the first actuator unit 200 in all of thethree graphs indicating the relationship between acceleration and timein FIG. 11. In the case of the uppermost graph and the second uppermostgraph among the graphs indicating the relationship between accelerationand time in FIG. 11, braking force is further generated by the secondactuator unit 300. With the braking force, acceleration of the vehiclegradually decreases.

In the case of the second uppermost graph and the third uppermost graphamong the graphs indicating the relationship between acceleration andtime in FIG. 11, increase in the braking force due to the prescribedfactor occurs in time T2, and therefore the braking force generated bythe first actuator unit 200 increases. The second uppermost graph andthe third uppermost graph indicate both the case where the prescribedfactor occurs in time T1, and increase in braking force actually occursin time T2, and the case where occurrence of the prescribed factor ispredicted in time T1, and the prescribed factor actually occurs in timeT2, or increase in the braking force occurs practically at the same timewith the prediction. In the case of the third uppermost graph among thegraphs indicating the relationship between acceleration and time in FIG.11, the magnitude of the negative jerk (inclination) generated by thesecond actuator unit 300 is reduced lower than that in the case of thesecond uppermost graph among the graphs indicating the relationshipbetween acceleration and time. In the case of the third uppermost graphamong the graphs indicating the relationship between acceleration andtime, the second actuator unit 300 does not generate the jerk.Accordingly, in the example shown in FIG. 11, in three graphs indicatingthe relationship between acceleration and time, the acceleration of thevehicle is an identical negative acceleration a1 in time T3. Thisindicates that regardless of the presence or the degree of change inbraking force by the first actuator unit 200, the time required untilreaching the same acceleration is the same. As a result, a similardeceleration feeling can be presented to the user.

On the other hand, when there is a change in the braking force by thefirst actuator unit 200, and the jerk to be generated by the secondactuator is not restrained, the time required until reaching the sameacceleration becomes shorter, or the negative acceleration a2, a3 intime T3 becomes smaller than the acceleration a1 as shown by the thickdotted lines in the second uppermost and third uppermost graphs amongthe graphs indicating the relationship between acceleration and time inFIG. 11. As a result, the deceleration feeling presented to the userbecomes too large.

Effects

In the present disclosure, jerk is controlled to achieve decelerationfeeling assumed to be expected by the user in the coasting state of thevehicle, and thereby achieves adequate ride comfort and operationfeeling of a vehicle. When braking force increases due to gear shiftingof the transmission or the like in particular, the jerk generated by thebrake or the like is reduced in order to reduce fluctuation indeceleration feeling and to restrain the ride comfort and the operationfeeling from deteriorating.

Although one embodiment of the present disclosure has been described inthe foregoing, the present disclosure can be regarded as a controlmethod of braking force executed by one or more computers included in abraking force controller, a braking force control program, acomputer-readable non-transitory recording medium storing the brakingforce control program, and a vehicle or the like mounted with a brakingforce control system, in addition to the braking force controller.

The present disclosure is useful for the braking force controllermounted on a vehicle or the like.

What is claimed is:
 1. A braking force controller mounted on a vehicleincluding a first actuator unit and a second actuator unit configured togenerate braking force, the braking force controller being configured tocontrol the braking force to be generated by the second actuator unit,when an operation amount of an accelerator pedal shifts to zero fromother than zero, and the vehicle is put in a coasting state because ofthe operation amount of the brake pedal being zero, the braking forcecontroller comprising a target jerk calculation unit, a first estimationunit, a second estimation unit, and a control unit, the target jerkcalculation unit being configured to calculate a target jerk that is ageneration target value of jerk when the braking force is generated inthe vehicle, the jerk being negative when a vehicle travel direction isdefined as a positive direction; the first estimation unit beingconfigured to determine whether or not a prescribed factor thatincreases the braking force generated by the first actuator unitcurrently occurs, and to estimate, when determining that the prescribedfactor occurs, an increment of the braking force due to the prescribedfactor; the second estimation unit being configured to determine whetheror not the prescribed factor occurs within a prescribed period frompresent time even when the prescribed factor does not currently occur inthe vehicle, and to estimate, when determining that the prescribedfactor occurs, an increment of the braking force due to the prescribedfactor; and the control unit being configured to determine, based on acalculation result of the target jerk calculation unit, that a sum ofthe negative jerk generated when the second actuator unit generates thebraking force, and the jerk generated by the first actuator unit whenthe prescribed factor does not increase the braking force, becomes thetarget jerk, wherein when the prescribed factor currently occurs oroccurs within the prescribed period, and the increment of the brakingforce due to the prescribed factor is larger than a prescribed value,the control unit corrects the determined negative jerk such that anabsolute value of the negative jerk becomes smaller, based on anestimation result of the first estimation unit or the second estimationunit.
 2. The braking force controller according to claim 1, wherein: thefirst actuator unit includes a transmission; the prescribed factorincludes gear shifting by the transmission; and the first estimationunit and the second estimation unit estimate an increment of the brakingforce due to the gear shifting by the transmission, based on at leastone of a current gear ratio of the transmission, and oil temperature ofthe transmission.
 3. The braking force controller according to claim 2,wherein the second estimation unit determines whether or not gearshifting of the transmission occurs within a prescribed period frompresent time, based on current speed, current acceleration, and currentgear shifting speed of the vehicle.
 4. The braking force controlleraccording to claim 1, wherein: the first actuator unit includes alock-up clutch; the prescribed factor includes engagement of the lock-upclutch; and the first estimation unit and the second estimation unitestimate an increment of the braking force due to the engagement of thelock-up clutch, based on at least one of a difference between speed ofan engine and speed of the transmission on the lock-up clutch side, andoil temperature of the lock-up clutch.
 5. The braking force controlleraccording to claim 4, wherein the second estimation unit determineswhether or not the engagement of the lock-up clutch occurs within aprescribed period from present time, based on current speed, currentacceleration, and current gear shifting speed of the vehicle.